A CD-R disk is a typical write-once optical disk, and a user can write data on the CD-R disk only once. However, when the data on the CD-R disk becomes unnecessary, it is not easy to erase the written data from the CD-R disk. Therefore, the CD-R disk is rendered unplayable by using a disposal method, such as artificially applying a stress to the disk (folding, breaking, or damaging the disk) or changing the media characteristics under high temperature condition, whereby secret information recorded on the disk is prevented from leaking.
However, the conventional data erasing method relating to the write-once optical disk has the following drawbacks.
1) Reliability is insufficient, that is, it is uncertain whether the disk is completely unplayable or not.
2) The cost is high.
3) Erasing of data limited to a specific recording area cannot be carried out.
4) Substances detrimental to the environment are released.
It is expected that the CD-R disk market will become widespread in the future and, therefore, development of a simple and low-cost method and apparatus for completely erasing recorded data from the CD-R disk has been desired.